Process for producing photovoltaic device

ABSTRACT

In the step of forming a microcrystalline i-type semiconductor layer by high-frequency plasma CVD, where an area of the parallel-plate electrode is represented by S; a width of the discharge space in its direction perpendicular to the transport direction of the belt-like substrate, by Ws; a width of a region formed by the parallel-plate electrode together with its surrounding insulating region, in its direction perpendicular to the transport direction of the belt-like substrate, by Wc; a width of the belt-like substrate in the direction perpendicular to its transport, by Wk; a distance between the parallel-plate electrode and the belt-like substrate, by h; a power density at which crystal fraction begins to saturate at predetermined substrate temperature, material gas flow rate and pressure, by Pd; and a high-frequency power, by P; these are set as follows: 
     2 h/ ( Ws−Wc )≧2.5, ( Ws/h )×2( Ws−Wk )/[4 h+ ( Ws−Wc )]≧10, and  P≧ (10/8)× Pd×S.   
     This enables formation of a microcrystalline semiconductor layer having less characteristics distribution in the width direction of a belt-like substrate, and photovoltaic devices having uniform photoelectric conversion efficiency can be mass-produced by a roll-to-roll system.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a process for producing a non-singlecrystal semiconductor type photovoltaic device by a roll-to-roll system.

[0003] 2. Related Background Art

[0004] Photovoltaic devices which are photoelectric conversion devicesthat convert sunlight into electric energy are put into wide use aspublic-purpose power sources for low-power supply such as electroniccalculators and wrist watches, and attract notice as practicabletechnique in future as substitute power generation means for what iscalled petroleum fuel such as oil and coal. Photovoltaic devices utilizephotovoltaic force attributable to, e.g., p-n junction of semiconductordevices. Semiconductors such as silicon absorb sunlight to producephotocarriers of electrons and holes by the aid of photon energy, andthe photocarriers are taken out to the outside by differences inchemical potential at the p-n junction region.

[0005] For the advancement of bringing photovoltaic devices intopractical use as their use for electric power, it is an importanttechnical subject to achieve cost reduction and make devices large-area,and various studies are made thereon. Researches are made on materialssuch as low-cost materials and materials with high photoelectricconversion efficiency. Such materials for photovoltaic devices mayinclude tetrahedral type amorphous semiconductors such as amorphoussilicon, amorphous silicon germanium and amorphous silicon carbide, andcompound semiconductors of Groups II-VI such as CdS and Cu₂S and thoseof Groups III-V such as GaAlAs. In particular, thin-film photovoltaicdevices in which amorphous semiconductors are used in photovoltaiclayers have advantages that they can provide films having larger areathan single-crystal photovoltaic devices, can be formed in a small layerthickness and can be deposited on any desired substrate materials, thusthey are regarded as promising.

[0006] However, in order to put such amorphous semiconductor typephotovoltaic devices into practical use as devices for electric power,it has been- a subject for studies to improve photoelectric conversionefficiency and improve reliability.

[0007] As a means for improving the photoelectric conversion efficiencyof the photovoltaic devices making use of amorphous semiconductors,various methods are available. For example, with regard to aphotovoltaic device that utilizes p-i-n type semiconductor junction, ap-type semiconductor layer, an i-type semiconductor layer, an n-typesemiconductor layer, a transparent electrode and a back surfaceelectrode which constitute the device must be improved incharacteristics for each layer.

[0008] As another method for improving photoelectric, conversionefficiency of photovoltaic devices, U.S. Pat. No. 2,949,498 disclosesuse of what is called a stacked cell, in which photovoltaic deviceshaving unit device structure are superposed in plurality. This stackedcell makes use of p-n junction crystal semiconductors. Its concept iscommon to both amorphous and crystalline, and is to make sunlightspectra absorb efficiently through photovoltaic devices having differentband gaps and make open-circuit voltage (Voc) higher so that electricitygeneration efficiency can be improved.

[0009] In the stacked cell, constituent devices having different bandgaps are superposed in plurality, and sunlight rays are absorbedefficienta at every part of their spectra so that photoelectricconversion efficiency can be improved. The cell is so designed that whatis called the bottom layer positioned beneath what is called the toplayer has a narrower band gap than the band gap of the top layerpositioned on the light-incident side of the constituent devicessuperposed.

[0010] Meanwhile, Y. Hamakawa, H. Okamoto and Y. Nitta report what iscalled a cascade type cell, in which amorphous silicon layers having thesame band gaps are superposed in multi-layer in such a way that noinsulating layer is provided between photovoltaic devices so that theopen-circuit voltage (Voc) of the whole device can be made higher. Thisis a method in which unit devices made of amorphous silicon materialshaving the same band gaps are superposed.

[0011] In the case of such stacked cells, too, like the case ofsingle-layer cells (single cells), in order to improve photoelectricconversion efficiency, characteristics must be improved for each layerof the p-type semiconductor layer, i-type semiconductor layer, n-typesemiconductor layer, transparent electrode and back electrode whichconstitute the photovoltaic device.

[0012] For example, in the case of the photoactivation layer, i-typesemiconductor layer, it is very important to make band-gap internallevels (localized levels) as less as possible to improve transportperformance of photocarriers.

[0013] With regard to-what is called doped layers such as the p-typesemiconductor layer and n-type semiconductor layer, it is firstlyrequired that their activated acceptors or donors are in a high densityand they can be activated at a small energy. This makes diffusionpotential (built-in potential) large when a p-i-n type junction isformed and enhances the open-circuit voltage (Voc) of the photovoltaicdevice, bringing about an improvement in photoelectric conversionefficiency.

[0014] It is secondly required that the doped layers, which basically donot contribute to the generation of photocurrent, do not obstruct as faras possible the light entering the photocurrent-generating i-typesemiconductor layer. Accordingly, in order to make the doped layers lessabsorb light, it is important to make their optical band gaps wide andto form them in small layer thickness.

[0015] Materials for doped layers having such characteristics include,e.g., Group IV semiconductor materials such as Si, SiC, SiN-and SiO, andthose having amorphous or microcrystalline form have been studied. Inparticular, Group IV semiconductor alloy materials having a wide opticalband gap have been considered preferable because of their smallabsorption coefficient; and microcrystalline or polycrystallinesemiconductor materials, because of their small absorption coefficientand small activation energy.

[0016] However, not a little lowering of carrier transport performanceand fill factor (FF) has occurred which is ascribable to latticematching and junction interfacial levels between the i-typesemiconductor layer and the microcrystalline or polycrystalline p-typesemiconductor layer, and its improvement has been a subject for studies.

[0017] Methods for solving such problems are under study. As an examplethereof, U.S. Pat. Nos. 4,254,429 and 4,377,723 disclose a method inwhich what is called a buffer layer(s) is/are provided at the junctioninterface(s) between the p-type semiconductor layer and/or n-typesemiconductor layer and the i-type semiconductor layer. At the junctioninterface between the p-type semiconductor layer or n-type semiconductorlayer and the i-type semiconductor layer, the former being formed ofamorphous silicon and the latter being formed of amorphous silicongermanium, many midgap levels are produced because of differences inlattice constant. Hence, they serve as the center of recombination atthe junction interface to make the lifetime of carriers short. Such abuffer layer is formed so that by the use of the buffer layer theband-gap internal levels can be reduced and the carrier transportperformance is not damaged to bring about an improvement incharacteristics.

[0018] Now, as a process for producing photovoltaic devices by formingsemiconductor functional deposited films continuously on a substrate, aprocess is known in which independent film-forming chambers for formingall kinds of semiconductor layers are provided, the respectivefilm-forming chambers are connected through gate valves by a load-locksystem, and the substrate is moved successively to the respectivefilm-forming chambers to form thereon the all kinds of semiconductors.

[0019] As a process which can improve mass productivity greatly, U.S.Pat. No. 4,400,409 discloses a continuous plasma CVD (chemical vapordeposition) process employing a roll-to-roll system. According to thisprocess, a continuous belt-like substrate is used as a substrate and thesubstrate is transported continuously in its lengthwise direction whiledepositing and forming semiconductor layers with any necessaryconductivity types in a plurality of glow discharge regions to formcontinuously devices having semiconductor junctions.

[0020] A deposited film forming apparatus of the above roll-to-rollsystem is constituted of a belt-like substrate wind-off chamber and awind-up chamber which are provided at both ends, respectively, andprovided between them deposited-film-forming chambers for forming aplurality of semiconductor layers by plasma CVD, which are arrangedthrough gas gates. Into the gas gates, a scavenging gas such as H₂ gasis introduced to form pressure barriers against their adjoiningdeposited-film-forming chambers so that the gas can be prevented fromdiffusing across the chambers. This is characteristic of theroll-to-roll system film-forming apparatus. Materials gases are fed toeach deposited-film-forming chamber, and high-frequency or microwavepower is applied thereto to cause discharge to take place in thedischarge space. Each deposited-film-forming chamber also has anevacuation means and a pressure control valve so that its inside can bemaintained at a vacuum state with a certain pressure.

[0021] In actual film formation, the continuous belt-like substrate isstretched over the wind-off chamber and the wind-up chamber, andsemiconductor layers can be deposited and formed successively in thedischarge spaces of the deposited-film-forming chambers while feedingand moving forward the substrate continuously.

[0022] In the roll-to-roll system, in view of its film-forming process,a film formed on the belt-like substrate has principally no differencein the transport direction of the belt-like substrate. In the widthdirection of the belt-like substrate, however, the film has a boundarycondition at its edge areas which is quite different from its centerarea, especially when a high-frequency power is used as excitationenergy and a parallel-plate electrode is used. This may cause a loweringof the density of excitation energy. Also, when a microcrystallinematerial is used in the buffer layer, a high feeding energy is requiredin order to form microcrystals, and hence a problem may occur seriouslywhich is the distribution of crystallinity in the width direction of thebelt-like substrate. Such a difference in crystallinity brings about adifference in band gaps and activation energy of films, and hence mayhinders the formation of desired junctions to bring about an increase inseries resistance of the photovoltaic device, resulting in a decrease inphotoelectric conversion efficiency because of a lowering of the fillfactor.

SUMMARY OF THE INVENTION

[0023] An object of the present invention is to provide, in such aroll-to-roll system, a process for producing a photovoltaic devicehaving a uniform photoelectric conversion efficiency, which isattributable to the formation of a microcrystalline semiconductor-layerhaving less characteristics distribution in the width direction of abelt-like substrate.

[0024] The present invention provides a process for producing aphotovoltaic device, comprising the step of forming a semiconductorlayer comprising a non-single crystal first-conductivity typesemiconductor layer, an amorphous i-type semiconductor layer, amicrocrystalline i-type semiconductor layer and a microcrystallinesecond-conductivity type semiconductor layer, on a belt-like substratewhile transporting the belt-like substrate continuously in itslengthwise direction;

[0025] the step of depositing a microcrystalline i-type semiconductorlayer in the above step being the step of introducing a film-forming gasinto a discharge space one face of which is formed by the belt-likesubstrate and simultaneously applying a high-frequency power from aparallel-plate electrode facing the belt-like substrate, to cause plasmato take place in the discharge space to form a deposited filmcontinuously on the surface of the belt-like substrate; and in thisstep;

[0026] where an area of the parallel-plate electrode is represented byS; a width of the discharge space in its direction perpendicular to thetransport direction of the belt-like substrate, by Ws; a width of aregion formed-by the parallel-plate electrode together with itssurrounding insulating region, in its direction perpendicular to thetransport direction of the belt-like substrate, by Wc; a width of thebelt-like substrate in the direction perpendicular to its transport, byWk; a distance between the parallel-plate electrode and the belt-likesubstrate, by h; a power density at which crystal fraction begins tosaturate at predetermined substrate temperature, material gas flow rateand pressure, by Pd; and the high-frequency power, by P; these being setas follows:

2h/(Ws−Wc)≧2.5,

(Ws/h)×2(Ws−Wk)/[4h+(Ws−Wc)]≧10, and P≧(10/8)×Pd×S.

[0027] In a preferred embodiment of the present invention, a value ofWc/h is 10 or more. Also, the belt-like substrate used in the presentinvention may preferably be electrically conductive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a schematic cross-sectional view of a plasma CVDsingle-cell continuous film-forming apparatus of a roll-to-roll system.

[0029]FIG. 2 is a schematic cross-sectional view of a high-frequencyplasma CVD film-forming chamber for forming the microcrystalline i-typesemiconductor layer according to the present invention, as its crosssection parallel to the transport direction of the belt-like substrate.

[0030]FIG. 3-is a schematic cross-sectional view of a high-frequencyplasma CVD film-forming chamber for forming the microcrystalline i-typesemiconductor layer according to the present invention, as its crosssection perpendicular to the transport direction of the belt-likesubstrate.

[0031]FIG. 4 is a graph showing the relationship between side-spaceratio h/d and crystal fraction (relative value) at different positionsof position m in width direction at the time of formation of themicrocrystalline i-type semiconductor layer according to the presentinvention is formed.

[0032]FIG. 5 is a graph showing the relationship between parallel-plateelectrode to belt-like substrate distance h and crystal fraction(relative value) at different positions of position m in width directionat the time of formation of the microcrystalline i-type semiconductorlayer according to the present invention is formed.

[0033]FIGS. 6A, 6B, 6C and 6D show graphs given by converting theabscissa in the FIG. 5 graph in accordance with discharge spacelength-width ratio Ws/h.

[0034]FIG. 7 is a graph given from the FIG. 5 graph by plotting therelationship between i) the value obtained by subtracting h fromwidth-direction position mo that provides a crystal fraction of 90% ormore of that at the center area and ii) d.

[0035]FIG. 8 is a graph showing changes in series resistance when in anSi single-cell type photovoltaic device a high-frequency power forforming a microcrystalline i-type Si layer is changed.

[0036]FIG. 9 is a diagrammatic cross-sectional view of the layerconfiguration of an Si single-cell type photovoltaic device of Example 1in the present invention.

[0037]FIG. 10 is a diagrammatic plan view of coupons prepared to makeevaluation on the photovoltaic device of Example 1 in the presentinvention.

[0038]FIG. 11 is a diagrammatic cross-sectional view of the layerconfiguration of an SiGe single-cell type photovoltaic device of Example2 in the present invention.

[0039]FIG. 12 is a schematic cross-sectional view of a plasma CVDcontinuous film-forming apparatus of a roll-to-roll-system, for formingsemiconductor layers of a photovoltaic device of Example 2 in thepresent invention.

[0040]FIG. 13 is a diagrammatic cross-sectional view of the layerconfiguration of an SiGe/SiGe/Si triple-cell type photovoltaic device ofExample 3 in the present invention.

[0041]FIG. 14 is a schematic cross-sectional view of a plasma CVDcontinuous film-forming apparatus of a roll-to-roll system, for formingsemiconductor layers of a photovoltaic device of Example 3 in thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] The present invention is characterized in that, in the step ofdepositing a microcrystalline i-type semiconductor layer according tothe roll-to-roll system, the shape of a discharge space, the width of abelt-like substrate and their conditions such as distance of these areset to have a predetermined relation. The relationship according to thepresent invention will be described below.

[0043] As stated previously, the distribution of crystallinity in thebuffer layer is concerned greatly with non-uniformity of characteristicsof the photovoltaic device. Accordingly, first, an experiment was madein order to examine changes in distribution of crystallinity inaccordance with conditions for the formation of buffer layer singlefilms.

[0044] In this experiment, when semiconductor layers are formed, aplasma CVD single-cell continuous film-forming apparatus 101 of aroll-to-roll system as shown in FIG. 1 was used and Si single cells wereproduced.

[0045] In FIG. 1, reference numeral 102 denotes a continuous belt-likesubstrate; 103, a wind-off chamber for the belt-like substrate 102; 104,a wind-up chamber for the belt-like substrate 102; and 105 to 108,semiconductor-layer-forming chambers, and more specifically, 105, forforming an amorphous n-type Si layer which is a non-single crystalfirst-conductivity type semiconductor layer; 106, for forming anamorphous i-type Si layer; 107, for forming a microcrystalline i-type Silayer; and 108, for forming a microcrystalline p-type Si layer which isa microcrystalline second-conductivity type semiconductor layer.Reference numerals 110 denote discharge spaces; 109, gas gates; and 111and 112, bobbins.

[0046]FIG. 2 is a structural cross-sectional view of thesemiconductor-film-forming chamber 106 for forming,a microcrystallinei-type Si layer, shown in FIG. 1, as its cross section parallel to thetransport direction of the belt-like substrate. FIG. 3 shows itsstructural cross section perpendicular to the transport direction. InFIGS. 2 and 3, reference numeral 201 denotes a vacuum chamber; 102, abelt-like substrate; 109, gas gates; 202, gate gas feed means; 203, adischarge box; 204, a belt-like substrate heating means (a lamp heater);205, material gas feed means; 206, a high-frequency parallel-plateelectrode (a cathode electrode);,110, a discharge space; 301, adischarge box bottom plate; and 302, a discharge box side plate.

[0047] Material gases are introduced into the discharge space 110through the material gas feed means 205. Then, a high-frequency power isapplied through the parallel-plate electrode 206 to decompose and excitethe material gases and cause plasma to take place. The belt-likesubstrate 102 is heated and kept at a prescribed temperature by means ofthe lamp heater 204. Thus, a functional deposited film can be formedcontinuously and in a large area.

[0048] In the present invention, as shown in FIG. 3, in the directionperpendicular to the transport direction of the belt-like substrate 102,a width of the discharge space 110 is represented by Ws; a width of aregion formed by the parallel-plate electrode 206 together with itssurrounding insulating region, by Wc; a width of the belt-like substrate102, by Wk; and a distance between the parallel-plate electrode 206 andthe belt-like substrate 102, by h. To simplify the description, an edgearea width d of the discharge box bottom plate is introduced by thefollowing-expression:

[0049] d−(Ws−Wc)/2.

[0050] As a distance from one width-direction end of the discharge spaceat an arbitrary position on the belt-like substrate 102, awidth-direction position m is also introduced (indicated in FIG. 3 isthe distance to the far edge of the belt-like substrate 102 ).

[0051] Crystallinity of microcrystalline film, i.e., the crystalfraction that indicates a ratio of amorphous component to crystallinecomponent is measured by spectral elipsometry. The spectral elipsometryis a process by which a difference in absorptivity of light wavesperpendicular to light waves parallel to the film surface is measuredand their absorption to a film formed on a non-light-transmittingsubstrate such as a metal substrate can be measured by utilizingreflection. In the spectral elipsometry, the dispersion of light wavesis measured, whereby the ratio of amorphous component to crystallinecomponent can be calculated from their wave-form separation.

[0052] (Experiment 1)

[0053] First, changes in distribution in accordance with the shape ofedge areas of the discharge box were examined. The size of d was changedin order to change the shape of ends of the discharge box. The dischargebox bottom plate 301 and the parallel-plate electrode 206 were changedin size to change the d to 5, 10, 20 or 40 mm. The distance ofthe-insulating region (the width of a space between an edge of thedischarge box bottom plate 301 and an edge of the parallel-plateelectrode 206 ) was fixed at 5 mm. As for each shape, films were formedunder conditions shown in FIG. 1. Belt-like substrate: SUS430

[0054] Wk=480 mm, Ws=500 mm, h=50 mm TABLE 1 High- frequency SubstrateGases Flow rate power Pressure temperature used (sccm) (W) (Torr) (° C.)SiH₄ 30 1,000 1.05 210 H₂ 1,500

[0055] In each d of the above, crystal fractions at width-directionpositions m=20, 40, 60, 80, 100 mm and 250 mm (the center area) weremeasured.

[0056] Results obtained are plotted with the values of h/d as abscissafor the value of m as a parameter, which are as shown in FIG. 4. Thenumbers of the ordinate indicated ratios to the crystal fraction atm=250 mm (the center area) that was regarded as 1. As can be seen fromFIG. 4, the crystal fraction (relative value) at the respectivepositions increases with an increase in h/d. The crystal fractionincreases greatly until h/d=2.5, and is seen to increase no longer whenh/d=5 or more. This means that a good crystallinity with lessdistribution can be attained at each width-direction position bycontrolling to 2.5 or more the h/d that represents the shape at sides ofthe discharge space.

[0057] (Experiment 2)

[0058] Next, what influences the changes in length-width ratio Ws/h ofthe discharge space may have was examined. The value of h was changed bychanging the discharge box side plate 302, to change the value of Ws/h.Films were formed under the same conditions as in Experiment 1 exceptfor those shown in Table 2. In the present experiment, only the value ofh was changed in the state the Ws was fixed, and hence the capacity ofthe discharge space changed in proportion to the h. In each condition,the pressure was fixed, and in order to make the residence time even,the flow rate of the used gas was made proportional to h as well as thehigh frequency power was also made proportional to h. On the basis ofthe results of Experiment 1, the value of d was also changed so that theh/d became constant at 2.5.

[0059] Belt-like substrate: SUS4302D

[0060] Wk=480 mm, Ws=500 mm, h=25 to 100 mm s=850 mm×450 mm TABLE 2High- frequency Substrate h Gases Flow rate power Pressure temp. (mm)used (sccm) (W) (Torr) (° C.) 25 SiH₄ 15 500 1.05 210 H₂ 750 50 SiH₄ 301,000 1.05 210 H₂ 1,500 75 SiH₄ 45 1,500 1.05 210 H₂ 2,250 100 SiH₄ 602,000 1.05 210 H₂ 3,000

[0061] For each h, the distribution of crystal fraction in the widthdirection was plotted to obtain the results shown in FIG. 5.

[0062] As can be seen from FIG. 5, the crystal fraction becomes morenon-uniform with an increase in the h, i.e., with a decrease in thelength-width ratio Ws/h.

[0063] In order to clarify the influence of this length-width ratio, thelength indicated on the abscissa was converted to obtain the resultsshown in FIG. 6. Those shown in FIG. 6 are revisions made by regardingthe length on the abscissa at the time of h=50 mm and Ws/h=10 as 1, thelength on the abscissa at the time of Ws/h=20 as 2, and the length onthe abscissa at the time of Ws/h=5 as ½.

[0064] As can be seen from FIG. 6, in the respective length-width ratiosthe graphs are well identical in shape.

[0065] The above results also allows to conclude as follows: Consideringon the basis of length-width ratio Ws/h=10, the crystal fraction at thewidth-direction position m=50 mm can be said in a different way that, atWs/h=20, it is identical to the crystal fraction at m=25 mm which is theposition half the m=50, and the crystal fraction at Ws/h=5 is identicalto the crystal fraction at m=100 mm which is the position twice them=50. More specifically, on the basis of the length-width ratio Ws/h=10,when the length-width ratio is changed, a width direction m′ thatprovides the same crystal fraction as that at the position of thewidth-direction position m at the length-width ratio=10 is seen to bem′=m×10/(Ws/h).

[0066] Using this relationship, the width-direction position standingwhen the length-width ratio is changed can be converted, thus thelength-width ratio Ws/h=10 is regarded as a basis.

[0067] Next, approximately what position was preferable for each edgearea of the belt-like substrate (its approximate distance from thedischarge box side plate 302 ) was examined. What is shown in FIG. 4 inExperiment 1 has led to a conclusion that the crystal fraction increaseswith an increase in h/d and shows no changes at a certain value orabove. Accordingly, taking note of the distribution of crystal fractionat various values of h/d, a width-direction position m₁ that provides acrystal fraction of 90% or more of that at the center area is seen to be50 mm or more. Here, even if only the Ws is extended to the widthdirection, it is considered that only the part where the distribution isuniform at the center area becomes larger and no change occurs in thedistribution at edge areas. Hence, it can be said that m₁ depends on h.In Experiment 1, the h is 50 mm, and hence it can be said that, at awidth-direction position m larger than h (m>h), a sufficiently largevalue of h/d provides a crystal fraction of 90% or more of that at thecenter area.

[0068] However, since the crystal fraction becomes more non-uniform witha decrease in the value of h/d, the crystal fraction of 90% or more ofthat at the center area can not be attained if only the condition of m>his fulfilled. To examine the relation of this deviation, in FIG. 5 whichis a graph of h/d=2.5 (constant), a width-direction position mo thatprovides the crystal fraction of 90% or more of that at the center areawas read from the plotted data (closest values were employed becauseactually the plotted data were discontinuous), and the relationshipbetween the value obtained by subtracting the value o f each achtherefrom (m_(o)−h) and the value of d was plotted to obtain the resultsshown in FIG. 7.

[0069] As can be seen from FIG. 7, a good proportional relation isshown, and its slope is substantially ½. That is, m_(o)=h+(d/2).

[0070] As can be seen from the foregoing, the crystal fraction of 90% ormore of that at the center area is attained at a width-directionposition m that satisfies m≧h+(d/2), so long as the value of h/d is 2.5or more. More specifically, a position meat an edge area of thebelt-like substrate 102 may be so set as to be m_(e)≧h+(d/2), wherebythe crystal fraction can be prevented from distributing. Also, as shownpreviously, the width direction m is regarded on the basis of Ws/h=10.Thus, taking account of these, the following expression is set up.

m _(e)=(Ws−Wk)/2≧[10/(Ws/h)]×[h+(d/2)],

[0071] therefore, (Ws/h)×2(Ws−Wk)/[4h+(Ws−Wc)]≧10.

[0072] Hence, the values of the chamber may be set as shown by the aboveexpression and also the value of h/d, i.e., 2H/(Ws−Wc), may be set to be2.5 or more. This enables deposition of a microcrystalline i-typesemiconductor layer having a uniform distribution of crystallinity.

[0073] (Experiment 3)

[0074] Even under the conditions described above, areas with a slightlylow crystallinity are present at edge areas with respect to the centerarea. Such areas with a low crystallinity affect the formation ofjunctions greatly, and cause, as a phenomenon, an increase in seriesresistance among characteristics of the photovoltaic device, to cause alowering of fill factors, resulting in a great lowering of conversionefficiency. The present invention has also solved such a problem.

[0075] The present inventors produced Si single cells at various appliedhigh-frequency power to examine changes in semiconductor at the centerarea and edge areas. To produce the Si single cells, the film-formingchamber used in Experiment 1 was used. Specific production procedure wasas described below.

[0076] First, in the wind-off chamber 103 having a substrate deliveringmechanism, a bobbin 111 was set which was wound with a belt-likesubstrate 102 (356 mm wide×200 m long×0.15 mm thick) comprised ofSUS4302D, having been degreased and cleaned thoroughly and on which, asa lower electrode, an aluminum thin film of 200 nm thick and a ZnO thinfilm of 1.2 μm thick had been deposited by sputtering. This belt-likesubstrate 102 was passed through the gas gate 109 and thedeposited-film-forming chambers 105 to 108 until it was wound around thebobbin 112 in the wind-up chamber 104 having a belt-like substratewind-up mechanism, where its tension was adjusted-so as to besubstantially free from sag.

[0077] In this state, the chambers 103, 105 to 108 and 104 wereevacuated to 1×10⁻¹ Torr or below by means of a vacuum pump (not shown).

[0078] Next, H₂ as a gate gas was flowed at a rate of 1,000 sccm foreach chamber through a gage gas feed pipe (not shown), and the belt-likesubstrate 102 was heated by the lamp heater. Then, materials gases werefed into the discharge space of each deposited-film-forming chamberthrough a material gas feed means. Conductance of a conductance valve(not shown) provided in a chamber (not shown) was so adjusted that thepressure in each chamber was set to a prescribed value. Thereafter, aprescribed high-frequency (13.56 MHz) power was applied to the cathodeelectrode of each deposited-film-forming chamber to cause discharge totake place in the discharge space.

[0079] Next, the belt-like substrate 102 was wound off continuously fromthe wind-off chamber 103, and a first-conductivity type semiconductorlayer, n-type Si layer, an amorphous i-type Si layer, microcrystallinei-type Si layer and a second-conductivity type semiconductor layer,microcrystalline p-type Si layer were superposed by forming themcontinuously on the belt-like substrate 102, which was then wound up onthe bobbin 112 of the wind-up chamber 104 having a belt-like substratewind-up mechanism.

[0080] Next, on the microcrystalline p-type Si layer, ITO (In₂O₃+SnO₂)as a transparent conductive layer was deposited in a thickness of 68 nmby sputtering using a different apparatus, and Al as a collectorelectrode was further deposited in a thickness of 2 μm by vacuumdeposition, thus photovoltaic devices were produced.

[0081] When the photovoltaic devices were produced, the high-frequencypower-applied for forming the microcrystalline i-type Si layer waschanged, and the photovoltaic devices obtained were compared on theircharacteristics. Other fabrication conditions (materials gases used, RFpower, pressure and substrate temperature) for forming the semiconductorlayers of the photovoltaic devices were as shown in Table 3. Ws=500 mm,h=50 mm, d=20 mm, S=850 mm×450 mm (each value is so set as to satisfythe results of

[0082] Experiment 2)

[0083] Belt-like substrate: SUS4302D, Wk=356 mm, thickness: 0.15 mm

[0084] Reflecting layer: Al thin film, thickness: 200 nm

[0085] Reflection enhancing layer: ZnO thin film, thickness: 1.2 μm

[0086] Transparent conductive layer: ITO thin film, thickness: 68 nmTABLE 3 Layer: High- Layer fre- Sub- thick- quency strate ness GasesFlow rate power Pressure temp. (Å) used (sccm) (W) (Torr) (° C.)Amorphous n-type Si layer: 125 SiH₄ 160 160 1.00 250 PH₃/H₂ 240 (PH₃:2%) H₂ 3,000 Amorphous i-type Si layer: 1,100 SiH₄ 350 1,400 1.10 200 H₂6,000 Microcrystalline i-type Si layer: 60 SiH₄ 30 600 to 1.05 210 1,200H₂ 1,500 Microcrystalline p-type Si layer: 80 SiH₄ 15 1,500 1.00 170BF₃/H₂ 110 (BF₃: 2%) H₂ 5,000

[0087] Samples were cut out at two places, the center area and an edgearea. The respective positions were width-direction position m=250 atthe center area and m=85 mm at the edge area.

[0088] With regard to the above photovoltaic devices, the dependence oftheir series resistance on applied high-frequency (RF) power is shown inFIG. 8. The series resistance is a property by which the quality ofperformance of a photovoltaic device as a diode comes out remarkably,and shows a low value when a good junction is formed. This seriesresistance is always affected by the bulk film characteristics or layerthickness of each semiconductor layer of the photovoltaic device. Theseries resistance of the photovoltaic device reflects remarkably thecrystallinity of the microcrystalline i-type layer which is a bufferlayer in the present Experiment.

[0089] As can be seen from FIG. 8, at applied RF power of from 1,200 Wto 800 W, the series resistance at the center area little changes and isalmost constant, but, at applied RF power further lowered to 600 W, theseries resistance increases though slightly. This is caused by the factthat, at applied RF power of from 600 W to 800 W, the crystallinityincreases with an increase in the applied RF power under suchconditions, but the crystallinity becomes saturated at applied RF powerof 800 W or above. Here, considering the applied RF power at the centerarea, the discharge space has the constitution of an idealparallel-plate electrode at its center area. Thus, an applied RF powerdensity Pd may be regarded as a value obtained by dividing an applied RFpower calculated geometrically by a parallel-plate electrode area S.More specifically, at the substrate temperature, material gas flow rateand pressure in the present Experiment, the crystal fraction saturatesat an applied RF power density Pd=800 W/(450 mm×850 mm).

[0090] Next, with regard to the series resistance of the photovoltaicdevice at its edge area of m=85 mm, it shows a much higher seriesresistance than that at the center area, when the applied RF power is600 W. This is caused by a low crystal fraction and an insufficientlayer thickness which come from the fact that a lowering ofelectric-field density due to the disorder of electric lines of force atan electrode edge area makes the applied RF power lower at the substrateedge area than the applied RF power density calculated geometrically.However, the series resistance is seen to decrease greatly with anincrease in the applied RF power. It decreases to substantially the samevalue as the series resistance at the center area when the applied RFpower is 1,000 W or above which is 10/8 time the 800 W at which thecrystal fraction saturates at the substrate temperature, material gasflow rate and pressure in the present Experiment. More specifically, theapplied RF power may be so set as to provide an RF power density of 10/8or more of the applied RF power density Pd at which the crystal fractionsaturates at predetermined substrate temperature, material gas flow rateand pressure, i.e., P≧(10/8)×Pd×S, whereby the crystal fraction at thesubstrate edge area can be prevented dramatically from lowering, so thata photovoltaic device having very uniform characteristics can beprovided.

EXAMPLE 1

[0091] As Example 1, an Si single-cell type photovoltaic device 901having the layer configuration as shown in FIG. 9 was produced. Thephotovoltaic device 901 was constituted of a conductive belt-likesubstrate 902 and formed superposingly thereon a back surface reflectinglayer 903, a reflection enhancing layer 904, an amorphous n-type Silayer 905, an amorphous i-type Si layer 906, a microcrystalline i-typeSi layer 907, a microcrystalline p-type Si layer 908, a transparentconductive layer 909 and a collector electrode 910.

[0092] To form the semiconductor layers, following the presentinvention, the plasma CVD single-cell continuous film-forming apparatusshown in FIG. 1 was used. A specific production procedure is describedbelow.

[0093] First, in the wind-off chamber 103 having a substrate deliveringmechanism, a bobbin 111 was set which was wound with a belt-likesubstrate 102 (356 mm wide×200 m long×0.15 mm thick) comprised ofSUS4302D, having been degreased and cleaned thoroughly and on which analuminum thin film of 200 nm thick as the back surface reflecting layer903 and a ZnO thin film of 1.2 μm thick as the reflection enhancinglayer 904 had been deposited by sputtering. This belt-like substrate 102was passed through the gas gate 109 and the deposited-film-formingchambers 105, 106, 107 and 108 until it was wound around the bobbin 112in the wind-up chamber 104 having a belt-like substrate wind-upmechanism, where its tension was adjusted so as to be substantially freefrom sag.

[0094] In this state, the chambers 103, 105, 106, 107, 108 and 104 wereevacuated to 1×10⁻¹ Torr or below by means of a vacuum pump (not shown).

[0095] Next, H₂ as a gate gas was flowed at a rate of 1,000 sccm foreach chamber through a gage gas feed pipe (not shown), and the belt-likesubstrate 102 was heated by the lamp heater so as to have the substratetemperature shown in Table 4, in each semiconductor layer formingchamber. Then, materials gases were fed into the discharge space of eachdeposited-film-forming chamber through a material gas feed means.Conductance of a conductance valve (not shown) provided between eachchamber and a vacuum pump was so adjusted that the pressure in eachchamber became the pressure shown in Table 4, using a pressure gauge(not shown) provided at the chamber. Thereafter, a high-frequency (13.56MHz) power as shown in Table 4 was applied to the cathode electrode ofeach deposited-film-forming chamber to cause discharge to take place inthe discharge space.

[0096] Next, the belt-like substrate 102 was wound off continuously fromthe wind-off chamber 103, and the n-type layer 905 as afirst-conductivity type semiconductor layer, the amorphous i-type layer906, the microcrystalline i-type layer 907 and the microcrystallinep-type semiconductor layer 908 as a second-conductivity typesemiconductor layer were formed continuously in order on the belt-likesubstrate 102 in the chambers 105, 106, 107 and 108, respectively, tosuperpose semiconductor layers in the layer thickness as shown in Table4. Then the substrate with layers thus formed thereon was wound up onthe bobbin 112 of the wind-up chamber 104 having a belt-like substratewind-up mechanism.

[0097] Next, on the microcrystalline p-type semiconductor layer 908, ITO(In₂O₃+SnO₂) as the transparent conductive layer 909 was deposited in athickness of 68 nm by sputtering using a different apparatus, thus thephotovoltaic device 901 was produced. The step of forming finally thecollector electrode 910 will be described in evaluation methodsdescribed later. The chamber 107 was set up to have the followingconditions.

[0098] Ws=500 mm, h=50 mm, d=20 mm, S=850 mm×450 mm (each value is soset as to satisfy the results of Experiment 2)

[0099] Belt-like substrate: SUS4302D, Wk=356 mm, thickness: 0.15 mm

[0100] Reflecting layer: Al thin film, thickness: 200 nm

[0101] Reflection enhancing layer: ZnO thin film, thickness: 1.2 μm

[0102] Transparent conductive layer: ITO thin film, thickness: 68 nmTABLE 4 Layer: High- Layer fre- Sub- thick- quency strate ness GasesFlow rate power Pressure temp. (Å) used (sccm) (W) (Torr) (° C.)Amorphous n-type Si layer: 125 SiH₄ 160 160 1.00 250 PH₃/H₂ 240 (PH₃:2%) H₂ 3,000 Amorphous i-type Si layer: 1,100 SiH₄ 350 1,400 1.10 200 H₂6,000 Microcrystalline i-type Si layer: 60 SiH₄ 30 1,000 1.05 210 H₂1,500 Microcrystalline p-type Si layer: 80 SiH₄ 15 1,500 1.00 170 BF₃/H₂110 (BF₃: 2%) H₂ 5,000

COMPARATIVE EXAMPLE 1

[0103] A to C three kinds of photovoltaic devices were produced asComparative Example 1 in the same manner as in Example 1 except for thefollowing.

[0104] Comparative Example 1-A: A photovoltaic device was produced inthe same manner as in Example 1 except that the distance h between theparallel-plate electrode and the belt-like substrate in the chamber 107for forming the microcrystalline i-type Si layer was changed to 100 mm(Ws/h=5) so as to be:

(Ws/h)×2(Ws−Wk)/[4h+(Ws−Wc)]<10,

[0105] and, in order to keep residence time, the flow rates of the gasesused were doubled and the applied RF power was doubled.

[0106] Comparative Example 1-B: A photovoltaic device was produced inthe same manner as in Example 1 except that only the bottom plate edgearea width d of the chamber 107 was set at 50 mm (h/d=1) so as to be h/d<2.5.

[0107] Comparative Example 1-C: A photovoltaic device was produced inthe same manner as in Example 1 except that only the applied RF power inthe chamber 107 for forming the microcrystalline i-type Si layer waschanged to 600 W or 800 W so as to be P<(10/8)×Pd×S.

[0108] (Evaluation)

[0109] Evaluation was made on the photovoltaic devices producedrespectively in Example 1 and Comparative Example 1. To make evaluation,two kinds of cell-pattern samples were prepared. One of them is a samplehaving subdivided as shown in FIG. 10, in order to well grasp thecharacteristics distribution of the photovoltaic devices, and ishereinafter called a coupon. The other is a sample not subdivided butprovided with a collector electrode formed of a copper wire coated withsilver around it and further coated with a carbon paste and having acell pattern with an area of 356 mm×240 mm, and is hereinafter called alarge-area cell.

[0110] A specific procedure for preparing the coupon is show below.

[0111] The photovoltaic devices produced in Example 1 and ComparativeExample 1 were each cut into a piece of 356 mm×120 mm in size. This ishereinafter called a slab.

[0112] The slab was put in an aqueous AlCl₃ solution electrolytic cell(not shown). The substrate side of the slab was set as the negative poleand the opposing electrode as the positive pole, and a positive voltageof 3.5 V was applied intermittently six times for 1 second for eachapplication to make electrolytic treatment. The aqueous AlCl₃ solutionwas set to have an electrical conductivity of 68 mS/cm (25° C.), and thearea of the opposing electrode was made identical to the slab area.Thereafter, the slab was taken out of the electrolytic cell, and thenwashed thoroughly with pure water to remove the electrolyte from itssurface, followed by drying in a hot-air oven at 150° C. for 30 minutes.

[0113] Next, FeCl₃•6H₂O was melted by heating, which was used as anetchant base solution, and fine acrylic resin particles of 5 μm inparticle diameter and glycerol were kneaded into the solution to preparean etching paste. Using this paste, an etched pattern 1002 as shown inFIG. 10 was printed in a line width of 1 mm on the transparentconductive layer of the slab by means of a screen printer (not shown).The pattern was formed in a layer thickness of 30 μm. Thereafter, in anIR oven (not shown), the slab was heated at a temperature of 170° C. for5 minutes. After the heating, the slab was taken out of the IR oven andcooled, followed by washing with pure water to remove the paste.Thereafter, the slab was dried in a hot-air oven at 150° C. for 30minutes, thus the etched pattern 1002 as shown in FIG. 10 was obtained.

[0114] Grid electrodes 1003 for collecting electricity were furtherformed as shown in FIG. 10, by screen printing of silver paste to makeup a coupon 1001.

[0115] The samples thus obtained were tested with a solar simulator (AM1.5, 100 mW/cm²) as irradiation light, to measure at 25° C. variouscharacteristic values (open-circuit voltage Voc, short-circuit currentdensity Jsc, fill factor FF and conversion efficiency).

[0116] Results obtained are shown dividedly for each of coupons andlarge-area cells. With regard to the coupons, the results are shown inTable 5 as a difference between the maximum value and the minimum value[(minimum value−maximum value)/maximum value) (%)] of eachcharacteristic value of the individual sub-cells. With regard to thelarge-area cells, the results of conversion efficiency are shown inTable 6 as a relative value standardized regarding the results ofExample 1 as 1. TABLE 5 Con- Applied version power effi- Ws/h h/d (W)Voc Jsc FF ciency Example: 1 10 2.5 1,000 −2.2% −1.8% −1.7% −1.8%Comparative Example: 1-A  5 2.5 2,000 −2.1% −1.8% −8.0% −8.4% 1-B 10 1.01,000 −2.1% −1.8% −3.2% −2.8% 1-C 10 2.5 600 −1.4% −1.8% −9.0% −8.1% 1-C10 2.5 800 −2.0% −1.8% −4.0% −4.1%

[0117] TABLE 6 Applied power Ws/h h/d (W) Conversion efficiency Example:1 10 2.5 1,000 1.00 Comparative Example: 1-A  5 2.5 2,000 0.96 1-B 101.0 1,000 0.98 1-C 10 2.5 600 0.97 1-C 10 2.5 800 0.97

[0118] As can be seen from Table 5, with regard to the coupons, thedevice of Example 1 has a remarkably superior uniformity in conversionefficiency compared with any of those of Comparative Example 1. As canalso be seen from Table 6, with regard to the large-area cells, too, thedevice of Example 1 is superior to any of those of Comparative Example1, and has achieved the uniformity in conversion efficiency at a highlevel.

EXAMPLE 2

[0119] As a second Example of the present invention, an SiGe single-celltype photovoltaic device 1101 having the layer configuration as shown inFIG. 11 was produced. In FIG. 11, reference numeral 1102 denotes aconductive belt-like substrate; 1103, a back surface reflecting layer;1104, a reflection enhancing layer; 1105, a first-conductivity typesemiconductor layer, amorphous n-type Si layer; 1106, an amorphousi-type Si layer; 1107, an amorphous i-type SiGe layer; 1108 an amorphousi-type Si layer; 1109, a microcrystalline i-type Si layer; 1110, asecond-conductivity type semiconductor layer, microcrystalline p-type Silayer; 1111, a transparent conductive layer; and 1112, a collectorelectrode.

[0120] The procedure for its production was basically the same as thatin Example 1. Under conditions shown in Table 7, used was a single-cellcontinuous film-forming apparatus of a roll-to-roll system as shown inFIG. 12, having deposited-film-forming chambers corresponding to therespective semiconductor layers.

[0121] In FIG. 12, reference numeral 1202 denotes a belt-like substrate;1203, a wind-off chamber for the belt-like substrate 1202; 1204, awind-up chamber for the belt-like substrate 1202; and 1205 to 1210,semiconductor-layer-forming chambers, in which reference numeral 1205denotes a chamber for forming the amorphous n-type Si layer 1105; 1206,a chamber for forming the amorphous i-type Si layer 1106; 1207, achamber for forming the amorphous i-type SiGe layer 1107; 1208, achamber for forming the amorphous i-type Si layer 1108; 1209, a chamberfor forming the microcrystalline i-type Si layer 1109; and 1210, achamber for forming the microcrystalline p-type Si layer 1110. Also,reference numerals 1212 denote discharge spaces; 1211, gas gates; and1213 and 1214, bobbins. The respective chambers 1203 to 1210 areconnected through the gas gates 1211 so that the discharge spaces arekept independent from one another. The chamber 1207 for forming theamorphous i-type SiGe layer is a chamber for forming deposited films bymicrowave plasma CVD. The chamber 1209 is set up to have the followingconditions.

[0122] Ws=500 mm, h=50 mm, d=20 mm, S=850 mm×450 mm (each value is soset as to satisfy the results of Experiment 2)

[0123] Belt-like substrate: SUS4302D, Wk=356 mm, thickness: 0.15 mm

[0124] Reflecting layer: Al thin film, thickness: 200 nm

[0125] Reflection enhancing layer: ZnO thin film, thickness: 1.2 μm

[0126] Transparent conductive layer: ITO thin film, thickness: 68 nmTABLE 7 Layer: High- Layer fre- Sub- thick- quency strate ness GasesFlow rate power Pressure temp. (Å) used (sccm) (W) (Torr) (° C.)Amorphous n-type Si layer: 125 SiH₄ 160 160 1.00 250 PH₃/H₂ 240 (PH₃:2%) H₂ 3,000 Amorphous i-type Si layer: 100 SiH₄ 45 140 1.05 270 H₂ 90Amorphous i-type SiGe layer: 800 SiH₄ 90 400 (μw) 0.01 380 GeH₄ 1151,200 H₂ 600 Amorphous i-type Si layer: 110 SiH₄ 100 150 1.05 300 H₂1,500 Microcrystalline i-type Si layer: 60 SiH₄ 30 1,000 1.05 210 H₂1,500 Microcrystalline p-type Si layer: 80 SiH₄ 18 1,200 1.00 230 BF₃/H₂450 (BF₃: 2%) H₂ 6,000

COMPARATIVE EXAMPLE 2

[0127] A to C three kinds of photovoltaic devices were produced asComparative Example 2 in the same manner as in Example 2 except for thefollowing.

[0128] Comparative Example 2-A: A photovoltaic device was produced inthe same manner as in Example 2 except that the distance h between theparallel-plate electrode and the belt-like substrate in the chamber 1209for forming the microcrystalline i-type Si layer was changed to 100 mm(Ws/h−5) so as to be:

(Ws/h)×2(Ws−Wk)/[4h+(Ws−Wc)]<10,

[0129] and, in order to keep residence time, the flow rates of the gasesused were doubled and the applied RF power was doubled.

[0130] Comparative Example 2-B: A photovoltaic device was produced inthe same manner as in Example 2 except that only the bottom plate edgearea width d of the chamber 1209 for forming the microcrystalline i-typeSi layer was set at 50 mm (h/d=1) so as to be h/d<2.5.

[0131] Comparative Example 2-C: A photovoltaic device was produced inthe same manner as in Example 2 except that only the applied RF power inthe chamber 1209 for forming the microcrystalline i-type Si layer waschanged to 600 W or 800 W so as to be P<(10/8)×Pd×S.

[0132] (Evaluation)

[0133] Evaluation was made on the photovoltaic devices of Example 2 andComparative Example 2 in the same manner as in Example 1 and ComparativeExample 1. Results obtained are shown in Table 8 (coupons) and Table 9(large-area cells). TABLE 8 Con- Applied version power effi- Ws/h h/d(W) Voc Jsc FF ciency Example: 2 10 2.5 1,000 −2.2% −3.0% −2.3% −2.4%Comparative Example: 2-A  5 2.5 2,000 −1.0% −2.9% −9.5% −11.8% 2-B 101.0 1,000 −1.9% −3.0% −3.8% −4.3% 2-C 10 2.5 600 −1.3% −3.0% −8.9%−10.1% 2-C 10 2.5 800 −1.7% −2.9% −4.0% −5.4%

[0134] TABLE 9 Applied power Ws/h h/d (W) Conversion efficiency Example:2 10 2.5 1,000 1.00 Comparative Example: 2-A  5 2.5 2,000 0.95 2-B 101.0 1,000 0.97 2-C 10 2.5 600 0.64 2-C 10 2.5 800 0.95

[0135] As can be seen from Table 8, with regard to the coupons, thedevice of Example 2 has a remarkably superior uniformity in conversionefficiency compared with any of those of Comparative Example 2. As canalso be seen from Table 9, with regard to the large-area cells, too, thedevice of Example 2 is superior to any of those of Comparative Example2, and has achieved the uniformity in conversion efficiency at a highlevel.

EXAMPLE 3

[0136] As a third Example of the present invention, an SiGe/SiGe/Sitriple-cell type photovoltaic device 1301 having the layer configurationas shown in FIG. 13 was produced.

[0137] In FIG. 13, reference numeral 1302 denotes a conductive belt-likesubstrate; 1303, a back surface reflecting layer; 1304, a reflectionenhancing layer; 1305, a bottom SiGe cell, which consists of anamorphous n-type Si layer 1308, an amorphous i-type Si layer 1309, anamorphous i-type SiGe layer 1310, an amorphous i-type Si layer 1311, amicrocrystalline i-type Si layer 1312 and a microcrystalline p-type Silayer 1313. Reference numeral 1306 denotes a middle SiGe cell, whichconsists of an amorphous n-type Si layer 1314, an amorphous i-type Silayer 1315, an amorphous i-type SiGe layer 1316, an amorphous i-typeSiGe layer 1317, a microcrystalline i-type Si layer 1318 and amicrocrystalline p-type Si layer 1319. Reference numeral 1307 denotes atop Si cell, which consists of an amorphous n-type Si layer 1320, anamorphous i-type Si layer 1321, a microcrystalline i-type Si layer 1322and a microcrystalline p-type Si layer 1323. A transparent conductivelayer 1324 and a collector electrode 1325 are further superposed thereonto make up the cell.

[0138] To form the semiconductor layers, used was a plasma CVDtriple-cell continuous film-forming apparatus employing a roll-to-rollsystem as shown in FIG. 14.

[0139] In FIG. 14, reference numeral 1402 denotes a belt-like substrate;1403, a wind-off chamber for the belt-like substrate 1402; 1404, awind-up chamber; and 1408 to 1423, semiconductor-layer-forming chambers,in which reference numerals 1408, 1414 and 1420 denote chambers forforming the amorphous n-type Si layers 1308, 1314 and 1320,respectively; 1409, 1411, 1415, 1417 and 1421, chambers for forming theamorphous i-type Si layers 1309, 1311, 1315, 1317 and 1321,respectively; 1410 and 1416, chambers for forming the amorphous i-typeSiGe layers 1310 and 1316, respectively; 1412, 1418 and 1422, chambersfor forming the microcrystalline i-type Si layers 1312, 1318 and 1322,respectively; and 1413, 1419 and 1423, chambers for forming themicrocrystalline p-type Si layer 1313, 1319 and 1323, respectively.Also, reference numerals 1405, 1406 and 1407 denote sections for formingthe bottom SiGe cell 1305, the middle SiGe cell 1306 and the top Si cell1307, respectively. Reference numerals 1425 denote discharge spaces;1424, gas gates; and 1426 and 1427, bobbins.

[0140] The procedure for its production was basically the same as thatin Example 1. The semiconductor layers were formed under conditionsshown in Table 10. The chambers 1412, 1418 and 1422 were set up to havethe following conditions.

[0141] Ws=500 mm, h=50 mm, d=20 mm, S=850 mm×450 mm (each value is soset as to satisfy the results of Experiment 2)

[0142] Belt-like substrate: SUS4302D, Wk=356 mm, thickness: 0.15 mm

[0143] Reflecting layer: Al thin film, thickness: 200 nm

[0144] Reflection enhancing layer: ZnO thin film, thickness: 1.2 μmTransparent conductive layer: ITO thin film, thickness: 68 nm TABLE 10Layer: High- Layer fre- Sub- thick- quency strate ness Gases Flow ratepower Pressure temp. (Å) used (sccm) (W) (Torr) (° C.) Amorphous n-typeSi layer: 125 SiH₄ 160 160 1.00 250 PH₃/H₂ 240 (PH₃: 2%) H₂ 3,000Amorphous i-type Si layer: 100 SiH₄ 45 140 1.05 270 H₂ 90 Amorphousi-type SiGe layer: 800 SiH₄ 90 400 (μw) 0.01 380 GeH₄ 115 1,200 H₂ 600Amorphous i-type Si layer: 110 SiH₄ 100 150 1.05 300 H₂ 1,500Microcrystalline i-type Si layer: 60 SiH₄ 30 1,000 1.05 210 H₂ 1,500Microcrystalline p-type Si layer: 80 SiH₄ 18 1,200 1.00 230 BF₃/H₂ 450(BF₃: 2%) H₂ 6,000 Amorphous n-type Si layer: 125 SiH₄ 160 160 1.00 250PH₃/H₂ 240 (PH₃: 2%) H₂ 3,000 Amorphous i-type Si layer: 100 SiH₄ 45 1401.05 270 H₂ 90 Amorphous i-type SiGe layer: 800 SiH₄ 90 400 (μw) 0.01380 GeH₄ 115 1,200 H₂ 600 Amorphous i-type Si layer: 110 SiH₄ 100 1501.05 300 H₂ 1,500 Microcrystalline i-type Si layer: 60 SiH₄ 30 1,0001.05 210 H₂ 1,500 Microcrystalline p-type Si layer: 80 SiH₄ 18 1,2001.00 230 BF₃/H₂ 450 (BF₃: 2%) H₂ 6,000 Amorphous n-type Si layer: 125SiH₄ 160 160 1.00 250 PH₃/H₂ 240 (PH₃: 2%) H₂ 3,000 Amorphous i-type Silayer: 1,100 SiH₄ 355 1,400 1.10 200 H₂ 6,000 Microcrystalline i-type Silayer: 60 SiH₄ 30 1,000 1.05 210 H₂ 1,500 Microcrystalline p-type Silayer: 80 SiH₄ 15 1,500 1.00 170 BF₃/H₂ 110 (BF₃: 2%) H₂ 5,000

COMPARATIVE EXAMPLE 3

[0145] A to C three kinds of photovoltaic devices were produced asComparative Example 3 in the same manner as in Example 3 except for thefollowing.

[0146] Comparative Example 3-A: A photovoltaic device was produced inthe same manner as in Example 3 except that the distance h between theparallel-plate electrode and the belt-like substrate in each of thechambers 1412, 1418 and 1422 for forming the microcrystalline i-type Silayers was changed to 100 mm (Ws/h=5) so as to be:

(Ws/h)×2(Ws−Wk)/[4h+(Ws−Wc)]<10,

[0147] and, in order to keep residence time, the flow rates of the gasesused were doubled and the applied RF power was doubled.

[0148] Comparative Example 3-B: A photovoltaic device was produced inthe same manner as in Example 3 except that only the bottom plate edgearea width d of each of the chambers 1412, 1418 and 1422 was set at 50mm (h/d =1) so as to be h/d<2.5.

[0149] Comparative Example 3-C: A photovoltaic device was produced inthe same manner as in Example 3 except that only the applied RF power inthe chambers 1412, 1418 and 1422 for forming the microcrystalline i-typeSi layers was changed to 600 W or 800 W so as to be P<(10/8)×Pd×S.

[0150] (Evaluation)

[0151] Evaluation was made on the photovoltaic devices of Example 3 andComparative Example 3 in the same manner as in Example 1 and ComparativeExample 1. Results obtained are shown in Table 11 (coupons) and Table 12(large-area cells). TABLE 11 Con- Applied version power effi- Ws/h h/d(W) Voc Jsc FF ciency Example: 3 10 2.5 1,000 −2.0% −2.6% −2.7% −2.6%Comparative Example: 3-A  5 2.5 2,000 −1.3% −2.5% −11.2% −13.4% 3-B 101.0 1,000 −1.8% −2.5% −4.9% −5.6% 3-C 10 2.5 600 −1.2% −2.7% −10.9%−12.1% 3-C 10 2.5 800 −1.6% −2.6% −6.5% −7.1%

[0152] TABLE 12 Applied power Ws/h h/d (W) Conversion efficiencyExample: 3 10 2.5 1,000 1.00 Comparative Example: 3-A  5 2.5 2,000 0.943-B 10 1.0 1,000 0.98 3-C 10 2.5 600 0.96 3-C 10 2.5 800 0.97

[0153] As can be seen from Table 11, with regard to the coupons, thedevice of Example 3 has a remarkably superior uniformity in conversionefficiency compared with any of those of Comparative Example 3. As canalso be seen from Table 12, with regard to the large-area cells, too,the device of Example 3 is superior to any of those of ComparativeExample 3, and has achieved the uniformity in conversion efficiency at ahigh level.

[0154] As described above, the present invention enables formation ofmicrocrystalline i-type semiconductor layers having uniformcharacteristics over a large area, and hence makes it possible toprevent large-area photovoltaic devices from having a low photoelectricconversion efficiency at the substrate edge areas, and to mass-produceuniform and good-quality photovoltaic devices in a good yield.

What is claimed is:
 1. A process for producing a photovoltaic device,comprising the step of forming a semiconductor layer comprising anon-single crystal first-conductivity type semiconductor layer, anamorphous i-type semiconductor layer, a microcrystalline i-typesemiconductor layer and a microcrystalline second-conductivity typesemiconductor layer, on a belt-like substrate while transporting thebelt-like substrate continuously in its lengthwise direction; the stepof depositing a microcrystalline i-type semiconductor layer in the abovestep being the step of introducing a film-forming gas into a dischargespace one face of which is formed by the belt-like substrate andsimultaneously applying a high-frequency power from a parallel-plateelectrode facing the belt-like substrate, to cause plasma to take placein the discharge space to form a deposited film continuously on thesurface of the belt-like substrate; and in this step; where an area ofthe parallel-plate electrode is represented by S; a width of thedischarge space in its direction perpendicular to the transportdirection of the belt-like substrate, by Ws; a width of a region formedby the parallel-plate electrode together with its surrounding insulatingregion, in its direction perpendicular to the transport direction of thebelt-like substrate, by Wc; a width of the belt-like substrate in thedirection perpendicular to its transport, by Wk; a distance between theparallel-plate electrode and the belt-like substrate, by h; a powerdensity at which crystal fraction begins to saturate at predeterminedsubstrate temperature, material gas flow rate and pressure, by Pd; andthe high-frequency power, by P; these being set as follows:2h/(Ws−Wc)≧2.5(Ws/h)×2(Ws−Wk)/[4h+(Ws−Wc)]≧10, and P≧(10/8)×Pd×S.
 2. Theprocess for producing a photovoltaic device according to claim 1,wherein a value of Wc/h is 10 or more.
 3. The process for producing aphotovoltaic device according to claim 1, wherein the belt-likesubstrate is electrically conductive.